The invention described and claimed herein is related to the invention set forth in U.S. patent application Ser. No. 07/812,192 filed contemporaneously herewith on Dec. 20, 1991, entitled "Surface Effect Dampers", which is hereby incorporated by reference.
One of the earliest patents relating to dampers employing hysteresis damping, that is the dissipation of translational energy by working of an elastomeric member, in U.S. Pat. No. 3,232,597 to Gaydecki. As a way of achieving a practical wearlife for his damper, Gaydecki sought to eliminate or, at least, minimize the frictional force component developed between the elements of his damper.
As described in the aboveidentified related application, eliminating totally the friction component of damping places severe limits upon the damper's design because a significant potential damping force has been eliminated. The approach taken in the aforementioned application and by Applicants herein, is to take advantage of the damping force available while minimizing the damage friction can produce.
For certain applications, it is desirable to produce one level of damping under certain circumstances and a second level of damping under other circumstances. One such application is in the area of railcar dampers. It is desirable to produce different levels of damping force for filled railcars than for empty ones. An increased damping force will be necessary to control the movement of the loaded railcars.
This invention provides a dual-rate surface effect damper for such applications. A cylindrical housing has bonded to a portion of its internal periphery a first liner having a first length and a first internal diameter for producing a first surface effect damping force opposing motion of a rubbee piston which has an interference fit with the liner. A second liner having a second length and a second smaller internal diameter is bonded to a second portion of the housing to produce a second greater surface effect damping force opposing motion of the rubbee piston. A third liner is provided between said first and second liner segments providing a smooth transition between the first and second segments.
It is an important aspect of the present invention to control the potentially damaging characteristics of the friction damping force component of the surface effect damper. Several elements are provided to permit this control. First, heat dissipative fins are provided on the external periphery of the housing as is suggested in the contemporaneously filed patent application. Second, cooling is provided internally to the rubbee piston by creating air flow to dissipate heat.
Third, an abrasion resistant elastomer is selected for each of the liner segments, in accordance with the teachings of the companion application. Fourth, the external surface of the rubbing piston is coated with a material to diminish its porosity and, hence, its abrasion producing proclivities. Finally, a lubricant is introduced between the rubbed member and the rubbee member to control the magnitude of the friction component. A lubricant which has been shown to have particularly useful properties in extending the wearlife of the elastomer is a (fluro)silicone lubricant which is filled with Teflon.RTM. particles and has dispersed therein molybdenum disulfide (MoS.sub.2). The ratio of filled silicone grease to MoS.sub.2 which appears optimum is on the order of 15 to 1, by weight.
Various other features, advantages and characteristics of the present invention will become apparent after a reading of the following invention.